This invention relates to filament-wound vessels and, more particularly, to an improved end fitting for a vessel which is adapted to contain corrosive and/or pressurized fluids.
A typical application for the invention is an accumulator or pressure control device for water systems dependent upon well water. Such a system includes a pipe extending into the underground water supply, a pump, and a reservoir tank which is connected to the service lines. Frequently, the tank is a metal container having no valve for pressurizing the tank with air and in which the air is merely trapped. In some installations, a valve, such as a regular tire valve, may be positioned at or near the top of the container and an outlet may be positioned near the bottom. A diaphragm may or may not be provided to separate the air from the water. A charge of air is introduced into the tank, usually occupying about one-half the volume of the tank and to a pressure sufficient to force water into the service lines connected thereto. A pressure switch senses the pressure within the tank or in the service line, as the case may be, and operates between limits, e.g., between 20 and 40 psi. If the pressure falls below 20 psi, the pump is activated and continues to operate until the pressure in the system is built up to 40 psi, when the pump is turned off by the pressure switch.
An acceptable prior art accumulator is set forth in U.S. Pat. No. 4,214,611, wherein the accumulator includes a pressure vessel having an inflatable bag therein which serves as a water-air separating diaphragm, with an inflating valve communicating with the interior of the bag and extending through one end of the tank. An inlet and outlet aperture is provided in the other end of the tank, and that aperture is in fluid communication with the water contained in the tank and the service system by means of a T-shaped fitting which is threaded into the aperture.
The tank or vessel disclosed in U.S. Pat. No. 4,214,611 is a unitary, seamless tank produced from glass fiber-reinforced resinous compositions which is produced in accordance with the process described in U.S. Pat. No. Re. 25,241 to Randolph, dated Sept. 11, 1962. The T-shaped fitting is an injection-molded fitting of conventional design. When the tank is pressurized, the threaded opening of the tank tends to enlarge radially relative to the neck of the threadedly received T-fitting. At the same time, the threaded neck of the T-fitting is urged axially outwardly by the pressure applied thereto. Furthermore, these pressure conditions are not static, but fluctuate as line pressure varies during water usage. Frequently, failure obtains by cracking of the tank around the opening or, more frequently, by stripping the threaded connection between the access opening and the T-fitting.